This application is based on Japanese application 214584/1999 and 222158/1999, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to an image forming apparatus such as a copying machine or a printer and a developing apparatus used for the image forming aparatus, and more particularly, to a developing apparatus using only toners for a developer and adapted to rotate, in introducing the toners into a developing area opposite to an image carrying member by a developing roller to perform development, the development roller to move upward from below in the developing area opposite to the image carrying member as well as to regulate by a regulating member the amount of the toners to be conveyed to the developing area by the developing roller under the developing roller, and an image forming apparatus using the developing apparatus.
2. Description of the Related Art
Conventionally known as a developing apparatus, used in an image forming apparatus such as copying machine or a printer, has been a developing apparatus using a mono-component developer containing no carriers and only tones in addition to a developing apparatus using a two-component developer containing toners and carriers.
An example of the developing apparatus using a mono-component developer containing only toners is one as shown in FIG. 1.
In the developing apparatus, toners t contained in a containing section 1a in an apparatus body 1, are fed to a toner supplying member 3, in a roller shape by a toner feeding member 2, and the toner supplying member 3 is rotated, to supply the toners t to a developing roller 4.
The developing roller 4 is rotated, to convey the toners t supplied in the above-mentioned manner. Further, a regulating member 5 is pressed against the surface of the developing roller 4, to regulate by the regulating member 5 the amount of the toners t to be conveyed by the developing roller 4 as well as to subject the toners t to triboelectric charging. The toners t thus regulated and charged are introduced into a developing area opposite to an image carrying member 6 by the developing roller 4, to perform development.
In the conventional developing apparatus, the developing roller 4 and the image carrying member 6 are so rotated as to move downward from above in the developing area where the developing roller 4 and the image carrying member 6 are opposite to each other, as shown in FIG. 1.
Depending on the type of the image forming apparatus, however, it is necessary to move the image carrying member upward from below in the developing area. For example, in a color image forming apparatus using a plurality of developing apparatuses respectively containing toners having different colors and so adapted as to form toner images respectively having the colors in an image carrying member by the plurality of developing apparatuses as well as to successively transfer the toner images to an intermediate transfer member from the image carrying member, the image carrying member must, in some cases, be moved upward from below in the developing area in order to make the color image forming apparatus compact.
Consider a case where the image carrying member is thus moved upward from below in the developing area. In a case where the developing roller is so rotated as to move downward from above in the developing area, when the developing roller is brought into contact with image carrying member to perform development, the toners stay in an upstream portion where the developing roller is in contact with the image carrying member. Accordingly, the toners spill outward, and a formed image is fogged. On the other hand, when the developing roller and the image carrying member are not brought into contact with each other to perform development, a leak is liable to occur between the developing roller and the image carrying member.
In recent years, developing apparatuses each adapted so as to rotate, when an image carrying member is moved upward from below in a developing area where a developing roller and the image carrying member are opposite to each other, the developing roller so as to move upward from below in the developing area have been proposed, as disclosed in JP-A-8-297411, JP-A-9-244406, and JP-A-1-171226.
When the developing roller is rotated to move upward below in the developing area a regulating member for regulating toners supplied to the developing roller must be provided under the developing roller.
When the regulating member is thus provided under the developing roller, however, many of the toners supplied to the developing roller are dropped upon being separated from the developing roller by its own weight before being introduced into the regulating member, so that the toners in a sufficient amount are not introduced into the developing area. Accordingly, the density of a formed image is decreased.
Therefore, a developing apparatus which is provided with a sealing member so as to be brought into contact with the surface of a developing roller on the upstream side in the direction of rotation of the developing roller from a regulating member for regulating the amount of the toners in the developing roller has been proposed, as disclosed in JP-A-10-171226.
Even when the sealing member is provided to be brought into contact with the developing roller on the ups side in the direction of rotation of the developing roller from the regulating member, the toners are not sufficiently held on the developing roller, and are dropped upon being separated from the developing roller before being introduced into the position of the regulating member. Accordingly, the density of a formed image is still decreased. Particularly when a solid image containing a high proportion of a block portion is formed, the density of the obtained image is decreased, and the image becomes blurred.
An object of the present invention is to prevent, in a developing apparatus for rotating, in introducing toners into a developing area opposite to an image carrying member by a rotating developing roller to perform development, the developing roller so as to move upward from below in the developing area opposite to the image carrying member as well as regulating by a regulating member the amount of the toners to be conveyed to the developing area by the developing roller under the developing roller, the toners supplied to the developing roller from being dropped upon being separated from the developing roller before being introduced into the regulating member, to introduce the toners in a sufficient amount into the developing area.
Another object of the present invention is to obtain, when an image is formed by an image forming apparatus using the above-mentioned developing apparatus, an image having a sufficient image density, and particularly to obtain, even when a solid image containing a large proportion of an image portion is formed, a good image having a sufficient image density without being decreased in density and blurred.
A first developing apparatus according to the present invention comprises a developing roller for conveying charged toners to a developing area opposite to an image carrying member with the toners held on its surface, the developing roller being rotated upward from below in the developing area; a regulating member for regulating the amount of the toners to be conveyed to the developing area under the developing roller; a plate-shaped charging member for charging the toners; and a voltage applying device for applying a voltage to the charging member.
A second developing apparatus according to the present invention comprises a developing roller for conveying charged toners to a developing area opposite to an image carrying member with the toners held on its surface, the developing roller being rotated upward from below in the developing area; a plate-shaped regulating member for regulating the amount of the toners to be conveyed to the developing area under the developing roller; a plate-shaped charging member for charging the toners, the charging member being positioned on the upstream side in the direction of rotation of the developing roller from the regulating member, an end, on the downstream side in the direction of rotation of the developing roller, of the charging member being brought into contact with the developing roller, and a distance d from a point at which the charging member starts to come into contact with the developing roller to a front end, on the downstream side in the direction of rotation of the developing roller, of the charging member being not less than 0.3 mm.
An image forming apparatus according to the present invention comprises the first or second developing apparatus, and an image carrying member. The image carrying member is moved upward from below in the developing area.
These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrates specific embodiments of the invention.